Mechanistic study of the effect of roller compaction and lubricant on tablet mechanical strength.

Heckel analysis, tablet tensile strength, and indentation hardness were determined for a series of sieved and roller compacted microcrystalline cellulose mixtures under both unlubricated and lubricated conditions with magnesium stearate. These results have been used to evaluate the loss of reworkability following roller compaction for microcrystalline cellulose and show the extent of impact on tableting properties when magnesium stearate is added intragranularly prior to roller compaction. While results consistent with traditional work-hardening are observed as shown by a modest increase in dynamic hardness and mean yield pressure for unlubricated, roller compacted microcrystalline cellulose, it is overshadowed by the overlubrication effect seen during roller compaction and in particular, the subsequent milling step. The common practice of lubricating the feedstock with magnesium stearate to avoid sticking of the material to the compaction rolls appears to be the major cause of decreased mechanical strength of the final compressed tablets.

Particle size limits to meet USP content uniformity criteria for tablets and capsules.

Content uniformity (CU) of pharmaceutical dosage units can be affected by active pharmaceutical ingredient (API) particle size and size distribution. Previous authors have estimated this impact but use of different particle size descriptors led to confusion and difficulty in applying the theoretical models developed. We show that when the same descriptors for particle size and distribution are used (i.e., median diameter on a weight basis (d(50)) and geometric standard deviation (sigma(g))), previously published models are consistent. The approach of Yalkowsky and Bolton4 [Pharm Res 7:962-966, 1990] is modified to use these descriptors and updated for current USP28/NF23 CU criteria. A nomograph is provided to allow easy estimation of an acceptable d(50) for a given dose and sigma(g). To test the model's validity, tablets were manufactured over a wide range of doses and assayed for CU. As predicted, %relative standard deviation (RSD) increased as dose decreased. However, for APIs that deviate significantly from the assumed log-normal distribution, sigma(g) is more appropriately described by the upper region of the API size distribution, presumably because large particles have greatest influence on CU. At very low doses, CU values deviate significantly from normality, consistent with the presence of single large API particles causing super-potent dosage units.